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This study provides an empirical assessment of energy use and greenhouse gas (GHG) emissions associated with high and low residential development. Three major elements of urban development are considered: construction materials for infrastructure (including residential dwellings, utilities, and roads), building operations, and transportation (private automobiles and public transit). Two case studies from the City of Toronto are analyzed. An economic input-output lift-cycle assessment (EIO-LCA) model is applied to estimate the energy use and GHG emissions associated with the manufacture of construction materials for infrastructure. Operational requirements for dwellings and transportation are estimated using nationally and/or regionally averaged data. The results indicate that the most targeted measures to reduce GHG emissions in an urban development context should be aimed at transportation emissions, while the most targeted measures to reduce energy usage should focus on building operations. The results also show that low-density suburban development is more energy and GHG intensive (by it factor of 2.0-2.5) than high-density, urban core development on a per capita basis. When the functional unit is changed to a per unit of living space basis the factor decreases to 1.0-1.5, illustrating that the choice of functional unit is highly relevant to a full understanding of urban density effects. DOI: 10.1061/(ASCE)0733-9488(2006)132:1(10) CE Database subject headings: Residential location; Emissions Energy consumption; Canada; Buildings, residential.

The retirement of aging concrete infrastructure is resulting in significant material flows of concrete debris in the economy. A proposed outlet for this debris is new concrete: the debris can be crushed into small particles and used in place of virgin aggregate. This form of recycling lessens use of aggregate resources, but its consequences are less clear in terms of energy use and greenhouse gas emissions. To examine these impacts, we develop life-cycle inventory models of the manufacturing of recycled concrete aggregate from debris. Results from these models are then used in life-cycle models of nonstructural concretes containing varying proportions of recycled concrete aggregate. For scenarios in which virgin and recycled aggregates are locally available, only 20% recycled aggregate substitution is beneficial. This corresponds to a modest reduction in energy use and greenhouse gas emissions: up to 15 MJ/m3 and 1.20 kg CO2-eq./m3 of concrete, respectively. Only when virgin aggregate must be transported large distances are higher levels of substitution beneficial, in terms of the metrics studied. [ABSTRACT FROM AUTHOR]

Two different sized hydropower projects in China, one with a capacity of 44 MW and the other of 3,600 MW, were examined through life-cycle assessment (LCA) from the perspective of both sustainability and environmental impact and the influence of project scale. Using the economic input-output based LCA approach, energy use and greenhouse gas (GHG) emissions were quantified. The resulting energy payback ratios were found to be 7 and 48, whereas the normalized GHG emissions were 44 and 6 gCO2 equivalent per kW h of electricity production, both in favor of the larger project. Compared with published data on other renewable and nonrenewable options, temperate hydropower, particularly large hydropower, is indicated as an efficient electrical source with relatively low GHG emissions. [ABSTRACT FROM AUTHOR]

The paper presents a life-cycle energy analysis (LCEA) to quantify energy expenditures in the fabrication, use, and end-of-life stages of the pipes of a water distribution system. The methodology incorporates the capabilities of environmental input-output life-cycle analysis to quantify the energy required to fabricate pipes. The EPANET2 hydraulic model is applied in conjunction with a pipe-aging model to calculate the theoretical energy recovery in the use stage. An exponential pipe-break model is applied to quantify the energy required to repair pipe breaks during the use stage of a system. Simple formulations are developed to estimate the energy required to dispose of and recycle pipes once their service period has expired. The LCEA methodology is then applied to the New York City (NYC) water supply tunnels example to quantify energy expenditures in four planning scenarios with 10-, 20-, 50-, and 100-year pipe replacement frequencies. The results of the NYC example highlight the tension between the energy costs incurred in the fabrication and end-of-life stages of a system and those incurred in the use stage. A pipe-replacement period roughly equal to 50 years yielded the lowest overall energy expenditure in the three life stages. A sensitivity analysis was carried out to assess the influence of uncertain system parameters on energy expenditure estimates. [ABSTRACT FROM AUTHOR]